Re: Aggregates and associated relational operators

From: Bob Badour <bbadour_at_golden.net>
Date: Fri, 5 Sep 2003 18:59:19 -0400
Message-ID: <oK96b.557$Lp.53402758@mantis.golden.net>

"Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message news:ry86b.30$pP2.101_at_news.oracle.com...
> Some time ago there has been already a small thread about broken symmetry
> among relational operators ("Naisetrac Product", which BTW should properly
> called "Tensor Product"). Recent discussion about "fundamental" aggregates
> satisfying identities like this:
>
> sum(a union b) = sum(a) + sum(b)

Am I missing something? I don't recall anyone suggesting the above identity, and it seems to me the identity would be:

sum(a union b) = sum(a) + sum(b) - sum(a intersect b)

Are you using multiset union?

> max(a union b) = max(max(a),max(b))

> prompts a related question:
> Why union operator is so special that it has associated aggregation? Is
> there anything similar to aggregation that is missing?

I do not understand the questions. Could you clarify them a little? Received on Fri Sep 05 2003 - 17:59:19 CDT